1. Field of the Invention
The present invention generally relates to an image forming method and apparatus for a printing machine a printer and the like and, more particularly, to an image forming method and apparatus in which ink is fixed on a recording medium such as print paper during or after formation of the ink image.
2. Description of the Related Art
In an image forming apparatus such as a printing machine, ink is used to print an image on a recording medium such as recording paper or film. Generally, ink used for printing does not dry rapidly since such ink contains solvents having a high-boiling point. Thus, the ink cannot be fixed on a recording medium in a short time. A problem arises in that a so-called set-off occurs when the recording media is laid on top of another immediately after printing. Additionally, there is a problem in that when recording is performed on both surfaces of the recording medium, it takes a long time to print on both surfaces since printing on one surface cannot be performed until the ink printed on the other surface is completely cured or dried.
In order to solve the above-mentioned problems, there are conventional ink fixing methods as described below.
(1) Oxidative Polymerization Drying Method
A long time is needed to dry ink since vehicle molecules in drying oil and polymerized oil or resin varnish are slowly oxidative-polymerized in the presence of oxygen. Accordingly, if the recording papers stick to one another after being printed, the drying time is further extended, resulting in occurrence of set-off or blocking. This may be a big problem in trying to achieve a high-speed printing operation. In order to eliminate this problem, a powder coating may be applied. However, there is a problem in that the powder is scattered around the image forming apparatus, resulting in an adverse effect to humans body.
(2) Photochemical Polymerization Drying Method
This method solidifies ink by using an ink that can be cured by an ultraviolet beam and irradiating an ultraviolet beam to an ink image after printing. There is a problem in practice in that an expensive ink and an expensive ultraviolet beam irradiating apparatus are required.
(3) Electron Beam Drying Method
This method solidifies ink by using an ink that can be cured by an electron beam and irradiating an electron beam to an ink image after printing. There is a problem in practice in that an expensive ink and an expensive electron beam irradiating apparatus are required.
(4) Heat Drying Method
In order to achieve rapid drying, a recording paper must be heated within a very short time after printing of the ink image. Thus, a high power heat source must be used which is expensive. Additionally, there is a problem in that so-called heat wrinkles occur in a recording paper due to evaporation of water contained in the recording paper.
In an ink fixing method disclosed in Japanese Laid-Open Patent Application No.2-16053, the drying time of the ink is shortened by transferring excessive ink on the recording paper to a transfer paper by laying the transfer paper on the recording paper. In this method, since a coloring agent is transferred from the recording paper to the transfer papers as well as the solvent, the transfer paper is required for each recording paper so as to prevent a reverse transfer of the coloring agent from the transfer paper to the recording paper. Thus, there is a problem of increased running cost. Additionally, the size of the printing apparatus is increased due to providing an additional space for accommodating a transfer paper roll. Further, since a part of the ink on the recording paper is transferred to the transfer paper, there is a possibility that concentration of the ink on the recording paper is reduced.
In an ink fixing method disclosed in Japanese Laid-Open Patent Application No.59-29197, a drying action of ink is promoted by applying, after printing, a liquid type dryer containing metallic salts of fatty acid as a primary component. In this method, there is a problem in that the drying time is extended when humidity is high or when the immersion water is emulsified in the ink or when printing is performed with an acid paper.
In an ink fixing method disclosed in Japanese Laid-Open Patent Application No.58-84794 (corresponding to Japanese Patent publication No.64-9959), ink is cured by extracting and removing a solvent (A) contained in a vehicle of the ink to dissolve a resin from the ink on a recording paper by using a solvent (B) which does not dissolve the resin and is not miscible with the solvent (A). When this method is use in practice, the recording medium (recording paper) is immersed in the solvent (B), or the solvent (B) is sprayed on the surface of the recording medium, or a roll carrying the solvent (B) is contacted to the recording medium. This is performed so as to supply a large amount of the solvent (B) on the surface of the recording medium. Accordingly, if a recording medium such as a recording paper which absorbs the solvent (B) is used, and if a solvent having a low-volatility is used for the solvent (B), a time period greater than that required for fixing the ink is needed to dry the recoding paper. On the other hand, if a solvent having a high-volatility is used foe the solvent (B), there is a problem with respect to environmental sanitation.
Additionally, this method uses a large amount of solvent, and requires a mechanism for applying the solvent (B) and a mechanism for collecting the applied solvent (B). Thus, construction of the printing apparatus becomes complex.
Further if water is used as the solvent (B), there is a problem in that the strength of the recording medium is decreased, the surface of the recording medium is deteriorated or the quality of the printed material itself is deteriorated.
Additionally, the solvent (B) may penetrate into the resin of the vehicle when the solvent (B) contacts the vehicle contained in the ink. In this case, the vehicle may become cloudy, and the resin layer of the cured ink may become brittle. Additionally, the image quality is deteriorated since clearness or transparency of the ink is reduced. Further, there is a problem in that a mechanical strength of the fixed ink film is decreased, and the ink film may peel off the recording paper due to friction.
In an ink fixing method disclosed in Japanese Laid-Open Patent Application No.54-49208, an oil base ink is used, and a drying action of the ink is promoted by contacting organic peroxide with the ink which has been transferred to the recording paper. In this method, since the ink is a special ink containing metallic salts of fatty acid, and the metallic salts of fatty acid gradually react with oxygen in the air, there is a problem in storing the ink for a long period of time.
Japanese Laid-Open Patent Application No.3-178478 discloses a recording apparatus. In the recording apparatus disclosed in this patent document, if an oil base ink is used, the ink cannot be fixed or dried and it takes a long time to dry the ink. Specially, if the recording papers are laid on one another after printing, this causes a set-off or blocking and the drying time is further extended. Thus, there is a problem in achieving a high-speed printing.
In an ink fixing method disclosed in Japanese Laid-Open Patent Application No.59-45157, a drying action of ink is promoted by applying porous fine powder onto a print surface so as to absorb solvent contained in the ink. However, a large amount of powder must be applied on the print surface so as to fix the ink. In this case, a large amount of powder is also fixed on the print surface. This causes deterioration of image quality. Additionally, there is an environmental sanitary problem in that the powder is scattered and float in the atmosphere.
Additionally, a surface of a recording medium may be protected after printing by a resin layer applied thereon. The resin layer may be also applied to provide a visual effect to the printed matter such as glossy surface, a mat surface or an embossed surface.
In a method for protecting a printed surface disclosed in Japanese Laid-Open Patent Application No.2-80279, a printed surface is protected by press coating a film after applying a liquid containing acrylic urethane type resin. In this method, a heat treatment process lasting about one hour is required to dry the liquid containing acrylic urethane type resin. This process is complex and an apparatus for performing this process is large. Additionally, there is a problem in that material cost is increased since a laminate film is needed. Further, this method is limited to a printed surface using a water base ink.
In a method for protecting a printed surface disclosed in Japanese Laid-Open Patent Application No.3-173646, water resistance and weather resistance are achieved for a printed surface of the print paper in an ink jet print apparatus. In this method, a first liquid containing a coloring agent and a second liquid are projected separately so as to transfer an ink mixture onto a print surface. However, since two different liquids are projected to form a single dot, a diameter of the dot is enlarged due to an offset of positions. This may deteriorate gradation of the image. Thus, positional accuracy is required for the two liquid drops. However, there is a problem in that image quality is affected by a thickness of the recording paper. Additionally, this method is limited for use with an ink jet printing method.
In a method for protecting a print surface disclosed in Japanese Laid-Open Patent Application No.4-21493, a glossy surface is provided to a desired area of a print surface by applying a film after applying varnish to the desired area and then peeled off the film. It takes about 15 hours at 40.degree. C. to evaporate solvent contained in the varnish. Thus, this method requires a long time and a complex system.
In a method for protecting a print surface disclosed in Japanese Laid-Open Patent Application No.5-269949, a laminate film is applied to the print surface with heat and pressure so as to provide a glossy and protected print surface. The laminate film comprises a resin layer formed by a polypropylene resin containing petroleum resin and an adhesive layer containing more than 25% of polyolefine resin. In this method, since a pressure of about 35 kg/cm.sup.2 with an elevated temperature of 100.degree. C. is needed to adhere the laminate film to the print surface, a large-scale manufacturing facility is required. Additionally, there is a problem in that material cost of the laminate film is high.
In a method for protecting a print surface disclosed in Japanese Laid-Open Patent Application No.8-39947, a mat processed laminate layer is formed on the print surface of the print paper. In this method, a transfer type laminate film is used which comprises a base material applied with a laminate layer. The base material is formed by a layered product comprising a polyester film and a mat processes polyolefine resin layer. Accordingly, the laminate film includes two films other than the laminate layer, and also includes the adhesive layer to adhere the laminate film. Thus, the material cost of the laminate film is increased. Additionally, processing speed of the lamination of the lamination film onto the print surface is as slow as 1 m/min. which provides low-productivity, and an additional process for peeling off the film is needed. Further, since the laminate layer is solid, there is a problem in that there is a low degree of adhesion with respect to a coarse print surface.
In a method for protecting a print surface disclosed in Japanese Laid-Open Patent Application No.54-120005, an ultraviolet cure type coating agent is coated on a print surface printed with an oil base ink, and the coating agent is dried to provide a coating film on the print surface. The coating agent comprises a composite including a prepolymer and a photosensitizer to which composite a resin or a resin acid of 0.5 to 10.0% is added. The prepolymer may include a prepolymer having a radical cross-linking ethylene unsaturated double bond. The prepolymer may be added with a monomer having a radical cross-linking ethylene unsaturated double bond. In this method, since the ultraviolet cure type coating agent is used, running cost and facility cost for a curing process is increased. Additionally, use of this method is limited to a print surface printed by an oil base ink.